1. Field of the Invention
The present invention is directed to a method and to an apparatus for the transport of pre-printed, web-shaped recording media, particularly continuous form paper in an electrographic printer. Paper, foil material, labels or other materials can thereby be employed as the web-shaped recording medium.
2. Description of the Related Art
The greatest variety of paper grades are employed when printing paper. What is referred to as margin-perforated paper is mainly employed in the electrographic high-performance printer field with printing outputs of more than 40 pages per minute. This paper has lateral holes at its longitudinal edges for transport and for monitoring the position of the paper. It is thereby driven by sprocket tractors that engage into the lateral transport holes. This paper often also has transverse perforations along which the individual pages are separated from one another.
The margin perforation is particularly employed when processing pre-printed paper. Given this paper, the information subsequently applied in the electrographic printer, for example data that are printed on a pre-printed form, should come to lie as exactly as possible at predetermined locations of the pre-printed form. For positionally exact printing, the position of the paper web in the conveying direction must be exactly adjusted to or, respectively, synchronized with the drive thereof or, respectively, the movement of the photoconductor drum.
For exact positioning of such paper, the first page of the paper web is placed exactly at a specific position with respect to the sprocket tractors. A page start mark of the pre-print or, respectively, the transverse perforation thereby exactly prescribes the beginning of the page. All further pages are automatically exactly positioned due to the constrained guidance by the tractor sprocket when the first page was properly inserted.
The feed of the perforated paper usually ensues in a specific grid corresponding to the hole spacings, for example in a xc2xd inch grid or in a ⅙ inch grid. The paper web is then not moved continuously but step-by-step by a multiple of the grid spacing.
There is frequently also the demand in the high-performance printing field to be able to employ roll paper that does not comprise such margin perforations in printers for continuous-form paper. Both economic as well as ecological considerations contribute to this demand. When printing margin perforated paper, namely, a processing step wherein the margin strips are removed from the printed page is necessary, whereby the waste that thereby arises must be disposed of.
For example, Published International application WO 95/19929 A1 discloses a printer that is suitable for processing roll paper without margin perforations. A first seating edge, which prescribes the lateral position of the paper, as well as stabilization rollers, and an under-pressure brake and a roller arrangement with a loop-drawing means are provided in this printer for the exact transport of the paper.
Even though continuous form papers both with as well as without margin perforation can be fundamentally processed with such a device, problems arise when printing forms. When one wishes to process pre-printed paper with such a printer, then no direct allocation of the pre-printed area to the information to be subsequently printed is possible. As a result thereof, the information to be subsequently printed cannot be fitted into the pre-print positionally correct.
Causes of mispositioning are, for example, fluctuations in the paper length that derive from different ambient temperatures or different degrees of moisture of the paper web. Such fluctuations can amount to up to a few millimeters per page. Deviations in the print image on this order of magnitude are not acceptable when printing forms.
Added thereto given tractor-less friction drives is the problem that the transport precision in the feed direction cannot always be adhered to. For example, slippage between the drive drum and the paper web or manufacturing tolerances of the drive mechanism can contribute thereto.
German Patent document DE 19 37 699 A likewise discloses a friction drive for data printers. A sensor that recognizes a pre-printed mark at the edge of the form is provided given this drive. A reallocation of the line height to the printing location is undertaken with the sensor result with the respective start of the form. What is disadvantageous about this drive is that a mark adapted to the sensor must be pre-printed at a specific position of the form so that the control function can be implemented.
U.S. Pat. No. 4,732,501 A discloses a printer wherein a recording medium web is transported with a first, slower speed in an insertion mode. In this mode, the operator can align the web within the drive before the printer switches into a printing operation mode with a second, higher transport speed. The switching between these two speeds can be controlled by a sensor that detects an edge of the recording medium web at a specific position. No specific measures, however, are provided in this printer for processing pre-printed recording media.
An object of the present invention is to provide a method and an apparatus for controlling a tractorless drive for web-shaped recording media with which pre-printed recording media can be transported in a positionally exact manner.
This object is achieved by the method for controlling a tractor-less recording medium drive in, in particular, an electrographic printer that outputs information on a pre-printed, web-shaped recording medium, whereby the recording medium comprises an identical optical marking page-by-page, including the following steps: a) the leading edge of the recording medium is placed at a predetermined insertion mark of the printer in an input region; b) the recording medium is transported a prescribed length along a conveying direction with a first, relatively slow speed by a transport motor; c) a sensor senses a predetermined region of the recording medium during the transport event and sends sensing signals to an evaluation means; d) the evaluation means investigates whether the sensing signals agree with the identifier of the marking; e) the transport length lying between two successive, identical markings is identified by the evaluation means as value for a page length; and e) the printing event is initiated with a second, relatively high transport speed and the transport is controlled with the identified value for the page length. The present invention also achieves the objectives by providing an apparatus for controlling a tractor-less recording medium drive in, in particular, an electrographic printer that outputs information on a pre-printed, web-shaped recording medium, whereby the recording medium comprises an identical optical marking page-by-page, having: a) control means that drive the transport motor such that the recording medium is transported a prescribed length along a conveying direction with a first, relatively slow speed; b) a sensor that senses a predetermined region of the recording medium during the transport event and sends sensing signals to an evaluation means, whereby c) the evaluation means investigates whether the sensing signals agrees [sic] with the identifier of the marking and the transport length lying between two successive, identical markings is identified as value for a page length; and d) the printing event is initiated with a second, relatively high transport speed and the transport is controlled with the identified value for the page length. Advantageous embodiments of the invention are the improvements to the method, including that the evaluation means comprises a memory in which at least one value for a standard page length is stored; and in that the value for a page length determined with the sensor is checked with the standard value or the standard values for plausibility before the determined value is identified as value for the page length. Following the identification of the page length, the recording medium is moved at least once opposite the conveying direction such that the first mark comes to lie in the active region of the sensor and, taking the identified page into consideration, is subsequently accelerated anew to the second mark, whereby the characteristic drive values thereby employed are stored for employment after a print stop. The sensor is preferably sensitized to the markings and/or to the background of the markings before it senses the recording medium for markings. The sensor ensues in that the recording medium is transported at least once in the direction of and opposite to the conveying direction, and the evaluation means checks during this forward and return motion to see whether and when the sensor outputs a signal. In one embodiment, the sensitization of the sensor ensues spectrally. The sensitization of the sensor may ensues in view of the shape of the marking. A sensor setting value determined during the sensitization is preferably stored. The information-containing components, particularly text components of pre-printed forms may be employed as the marking. The recording medium is typically paper.
It is provided in the invention to apply the leading edge of the pre-printed web of the recording medium provided with markings to a predetermined insertion mark in an input region of the printer. Subsequently, the recording medium web is transported a predetermined length along a conveying direction by a transport motor with a first, relatively low speed. A sensor thereby senses a predetermined region of the paper and sends sensor signals to an evaluation means. This evaluates the signals and checks whether they can be allocated to a predetermined mark. The transport length lying between two successive marks is then identified by the evaluation means as a value for a page length. Finally, the printing event is initiated with a second, relatively high transport speed and controlled with the identified value for the page length.
What the invention enables is that the drive for the web of the recording medium is already synchronized to the page length after a feed of one page. Positional deviations of the web that occur due to imprecise insertion of the paper web or due to increased slippage between the drive and the web are thereby already compensated after the first printed page. As a result of the invention, it is also possible to transport recording medium webs that contain indefinite pre-prints in a positionally exact manner. For example, the pre-prints can be indefinite in terms of type, color, shape, the size (length) or the position on the recording medium. The control requires only a negligible time for transient response. Maculature, i.e. excess, unprinted paper is largely avoid as a result thereof. The printing already ensues in a positionally exact manner within the pre-print with the first printed page.
In a preferred exemplary embodiment of the invention, the evaluation means comprises a memory in which at least one value for a standard page length is stored. The value for a page length determined with the sensor is checked against the standard value or the standard values for plausibility before the identified determined a value is identified as value for the page length. As a result thereof, it is possible to synchronize the drive exactly with the page length of the pre-print even when the page length deviates from the theoretical rated value.
In another advantageous embodiment of the invention, the sensor is sensitized for the markings and/or for the background of the markings. It is also advantageous to arrange the sensor so as to be displaceable transversely relative to the recording direction. The mark can then lie at an arbitrary location of the form. Even constituent parts of the form such as texts, graphics or window cut-outs can then be employed as a mark. The sensor of the invention can thus be adapted to the respective content of the form in that it is sensitized for a selected item of information.
In particular, the sensor can be of an optoelectronic type; the sensitization in a preferred exemplary embodiment then ensues for specific colors of the background or, respectively, of the mark. Alternatively or additionally, the sensitization of the sensor can also ensue in view of a geometrical shape of the markings or in view of the surface structure of the recording medium web. For example, the marks can thereby be notches provided in paper webs or window cut-outs in form originals. A sensor setting value determined in the sensitization is preferably stored and re-employed for later measurements.
The sensitization of the sensor preferably ensues in that the paper is transported at least once in the conveying direction and once opposite the conveying direction, whereby the evaluation means checks during this forward and return motion whether and when the sensor outputs a signal. It can thereby be provided that a plurality of cycles or forward and return motions are implemented and that a setting value at the sensor is modified after every cycle. The sensor setting values that are finally determined can then be stored and re-employed for later sensitization events. A self-learning system can thereby be generated in that a certain plurality of the setting values that are employed most often and/or most recently is employed at the beginning of a sensitization procedure.
What is particularly achieved with the inventive starting procedure is that the printing event can begin with the first page that follows the page required for the sensitization of the sensor.
The inventive procedure can be largely automated. Operating errors upon insertion of the paper are thereby largely precluded or, respectively, can be compensated. The procedure requires only little time, as a result whereof the effective printing time of the printer is high.